The present invention relates to process variable transmitters of the type used to monitor fluids in a process plant.
Process variable transmitters are used to monitor process variables associated with fluids such as slurries, liquids, vapors and gasses in chemical, pulp, petroleum, gas, pharmaceutical, food and other fluid processing plants. Process variables include pressure, temperature, flow, level, pH, conductivity, turbidity, density, concentration, chemical composition and other fluid properties. A process variable transmitter either includes or is connected to a sensor that senses the process variable and provides an output representing the process variable. The sensor output is connected to signal processing circuitry. Signal processing circuitry typically includes a damping time adjustment for the transmitter output which can be manually set, either locally or remotely. If a transmitter""s damping time setting is set high to strongly limit noise, then the transmitter output will respond more slowly when the sensed process variables changes. If the transmitter""s damping time is set low so that the transmitter""s output responds more quickly, then more noise will pass through from the sensor output to the transmitter output. Other signal filtering which reduces noise tends to introduce more time delay in the transmitter output relative to the process variable.
In the present invention, a filter automatically adjusts its bandwidth based on noise detected in a sensor output in a process variable transmitter. The process variable transmitter provides a damped transmitter output representing a process variable sensed by a sensor. When the transmitter senses higher sensor noise levels, it automatically decreases the filter bandwidth to damp noise in the transmitter output. When the transmitter senses lower sensor noise levels, it automatically increases the filter bandwidth to provide faster response to changes in the process variable.